This disclosure pertains to a transportable sewage container, and in particular to a sewage container intended for servicing portable toilets.
Portable toilets are a feature of construction sites and certain other temporary workplaces, and also of transient public events such as festivals and some sporting occasions. To service these toilets, it is necessary not only to transport them to and from sites where they are used; it is also necessary to transfer accumulated waste into a holding tank, which is transported to a treatment plant for proper disposal. Usually, the same vehicle (usually a flatbed truck) is used to transport both the toilets and the holding tank. Waste is transferred from the toilets to the holding tank by means of a pump that evacuates the holding tank to a vacuum of at least about 12xe2x80x3 of mercury. If the portable toilets are at a particular site for an extended time, they may need periodic servicing. Otherwise, they would be serviced at a central location, which may or may not be the location of the treatment plant. In any event, it is often convenient to be able to transport both the waste and the toilets themselves simultaneously on the same vehicle.
The ideal shape for a vessel needing to withstand a high pressure differential is a perfect sphere. A convenient way of describing a general configuration of a three-dimensional vessel is its aspect ratio, which may be defined as the ratio of the size of an object measured in two orthogonal dimensions. Clearly, a spherical vessel has an aspect ratio of 1, since it measures the same distance across in all dimensions. A cubic vessel also has an aspect ratio of 1. While not as strong as a sphere, it is stronger than a comparably shaped vessel with an aspect ratio greater than 1. As a rule of thumb, it may be stated that for any two vessels with comparable shapes and volumes but different aspect ratios, the one having a higher aspect ratio will be weaker with respect to pressure differential, all other factors being equal. A given object may have different aspect ratios depending on the directions of measurement.
It has hitherto been a feature of the aforementioned sewage holding tanks that they are generally cylindrical in shape to provide maximum strength, and do not have an aspect ratio greatly exceeding 1. They can be considered the best practical approximation to a sphere. A customary holding tank occupies a significant area of the truck bed, which obviously limits how many portable toilets can be accommodated. It is possible to envisage a low-profile holding tank occupying substantially the entire area of the truck bed, the tank itself having a flat cargo-bearing surface similar in area to that of the truck bed.
Conventional holding tanks typically have a low aspect ratio, and occupy a smaller area than the envisaged low profile tanks, but are not configured to support additional cargo.
Sometimes dedicated tanker trucks are used for carrying waste, having no additional cargo area for portable toilets. The evacuable, waste-containing portions of these tanker trucks are generally cylindrical. While their dimensions vary, the greatest aspect ratio (in this case evacuable cylinder length divided by diameter) is typically less than 3.
Typically, a flatbed truck carrying a conventional holding tank might have additional space for two portable toilets, while the envisaged low profile holding tank would provide space for at least four. In many situations this would be a distinct economic advantage, since it could cut to a half or a third the number of necessary trips, representing a considerable saving in time and labor.
There is therefore a need for a low profile holding tank configured to provide increased cargo carrying space. Such a configuration must necessarily have an aspect ratio significantly greater than 1, and it would normally be expected to be too weak to withstand the required evacuation. Therefore, there is further a need for a low profile holding tank capable of withstanding such evacuation.
The holding tank of the invention has a length and width conforming generally to the area of cargo space of a vehicle such as a flat bed or similar truck, and a height much less than the length or width. Consequently, the holding tank has an aspect ratio which may be as high as 24. The holding tank has a floor, walls, and a flat top or deck and is made from mild steel sheet stock.
An internal reinforcement is provided which allows relatively light sheet stock to be used for fabricating the holding tank. The reinforcement includes reinforcement strips inside the floor, support pillars attached to the reinforcement strips, and support strip attached atop the support pillars for absorbing pressure from the deck when the holding tank is evacuated.
Since the flat deck approximates the area of the truck bed, the low-profile holding tank essentially provides the same space for carrying cargo; the holding tank itself therefore uses up no cargo space, and additional space is therefore available for other payload. In particular, the freed up space can be used for transporting more portable toilets per trip than would otherwise be possible.
FIG. 1 is a partially cut-away perspective view of a low profile holding tank for a transportable sewage system.
FIG. 2 is a top plan view of the holding tank of FIG. 1.
FIG. 3 is a side elevation of the holding tank of FIG. 1.
FIG. 4 is an end elevation of the holding tank of FIG. 1.
FIG. 5 is a side elevation of a support assembly of the holding tank.
FIG. 6 is a schematic of the transportable sewage system connected to a portable toilet.
FIG. 7 is a side view of the transportable sewage system aboard a vehicle.
FIG. 8 is a rear view of the transportable sewage system aboard the vehicle.